Metal 3D printing is carried out by fusing powdered metal particles together to create an object in a successive layer by layer printing process. The particle properties are very important for successful metal 3D printing. Similar size, perfectly spherical shape of same diameter, and quality are intrinsic factors which affect the 3D printing process. Therefore it is necessary to manufacture consistent metal particles so that the printed part exhibits perfect density at all cross-sections.
There are numerous processes for manufacturing metal 3D printing powders. First we will understand the term atomisation and then have a look at some of these methods.
Atomisation is the process of transforming a solid, liquid or solution form into fine particles or droplets in a surrounding gas or vacuum.
The properties of the resulting particles or droplets are strongly affected by the size of the atomiser, properties of the material (solid or liquid) and properties of the gaseous medium into which the liquid is disintegrated.
Manufacturing Metal 3D Printing Powder
Gas atomisation is the most common method for manufacturing metal 3D printing powder of high quality. The feedstock is melted under an inert gas blanket or under vacuum. A gas then forces the molten alloy to pass through a nozzle where high velocity air, Nitrogen, Helium or Argon gas disintegrates the flowing molten metal fragmenting it into fine droplets or particles of powder. These droplets cool down while falling down in the atomising tower. These droplets or particles are mostly spherical with a small amount of asymmetrical particles.
Along with the particles, a separate particle called as satellite is also observed. A satellite is a small particle which binds to a larger particle while solidification. The size of the particles ranges from 0 to 500 microns, Yield within 20 to 150 microns range varies from 10% to 50% of total.
This process is mostly used for metals like Stainless Steel, Tools Steel, Iron, Nickel and Copper alloys. It is also used for Titanium and Aluminium alloys.
Water atomisation process is similar to gas atomisation process, with the only difference being the use of water in place of the high velocity gas as the atomising agent. This process is comparatively cheaper than gas atomisation.
This method is preferred for unreactive materials such as steels. But this process generally produces irregular shaped particles. Metals and alloys which do not react chemically with water.
Plasma atomisation is a comparatively new technique to manufacturing metal 3D printing powder of superior quality. It was patented by PyroGenesis in 1995. This process can manufacture powders which are small, uniform, fully dense and spherical metal powders which flow like water. A wire feedstock is fed directly into a plasma torch. The torch along aided by other gases, atomise the metal to form a powder. The size ranges from 0 to 200 microns. This process is restricted to alloys or only for ductile metals, i.e., which can be drawn out into wires.
EIGA (Electrode Induction melting Gas Atomisation)
Electrode Induction melting Gas Atomisation (EIGA) is most commonly used for manufacturing metal 3D printing powder from Titanium. It is used in case of reactive metals.
The feedstock is in the form of bars of metal. They are rotated at a high velocity and the n melted with the help of an induction coil. The molten metal flows down to the nozzle and out on a stream of gas for atomisation.
The particle size is 0 to 500 microns and powder is similar to gas atomisation. This process is relatively cheap and perfect for small batch production. It can create really fine powder.
PREP (Plasma Rotating Electrode Process)
This process is similar to EIGA. The only difference is that the rotating metal is melted only on contact with a plasma
The particles are extremely spherical and the cost can be pretty high.
In this method specifically used by LPW. This method is used to transform regular powders, produced during traditional metal crushing methods or during spray and sintering methods, into spherical powder.
The powder is fed from the top under gravity and is sprayed using plasma through various nozzles depending on the type of powder and its properties. Individual powder particles are fully melted and then formed into a perfect spherical particle which is completely dense. Special care is taken to avoid surface contamination by vaporising the impurities.
Rotating Disk atomisation
Rotating Disk atomisation is one of the easiest methods of manufacturing metal 3D printing powder. It can be considered as an alternative between Gas and Plasma atomisation. The powder produced through this process is more spherical that gas atomisation but has a lower quality compared to plasma atomisation.
This process is cheaper than both PREP and Plasma atomisation. It is suited for less reactive alloys with low melting temperatures.
Above listed methods are some of the most popular methods of manufacturing metal 3D printing powder.
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